Niobium-titanium chromium alloy



United States Patent 3,6435% NIQBEUM-TlTANlUM CHROMIUM ALLGY Hugh 3.Hix, Wiimingten, Deb, assignor to E. I. du Pont de Nemonrs and Company,Wilmington, Del., 2 corporation of Delaware No Drawing. Fiied Sept. 23,1959, Ser. No. 841,68 7 Claims. (Cl. 75-174) This invention pertains tonovel niobium base alloys, and more particularly to outstanding hightemperature strength and oxidation resistant, ternary alloys containingniobium, titanium, and chromium.

In present-day industry there is an ever-increasing need for metalswhich are utilizable at very high temperatures. This need has taken onconsiderable importance as a result of developments in jet engineaircraft and the field of atomic power. high temperature metals are alsoemployed in gas turbines of all types, dies for high temperature workingof metals, high temperature reactors, and the like. For a metal to besuitable as a material of construction in high temperature equipment, itmust possess, in addition to a high melting point, strength andoxidation resistance at the operating temperatures of the equipment.Furthermore, the metal must be ductile in order to permit itsfabrication. It is, therefore, an object of this invention to provideimproved, workable alloys which possess unusually high oxidationresistance and strength at elevated temperatures. It is a further objectto provide a metal alloy suitable as a material of construction in hightemperature equipment of all types.

It has now been found that workable alloys possessing unusually highcorrosion resistance and strength at high temperatures can be producedby alloying titanium, chromium, niobium, and the specified optionalelements in the amounts set forth herein. It is, therefore, an object ofthis invention to provide improved, workable alloys which possessunusually high oxidation resistance and strength at elevatedtemperatures. It is a further object to provide an alloy suitable as amaterial of construction in high temperature equipment of all types.

' The alloys of this invention comprise niobium base compositionscontaining about 30% by Weight of titanium, about 130% by weight ofchromium, and the balance being essentially niobium in an amount of atleast 50% by weight.

In addition to the above-named essential elements, the alloy may containabout 07% of aluminum, about 02% carbon, about 02% cobalt, about 07%iron, about 07% manganese, about 02% nickel, about 02% silicon, about07% tantalum, about 07% tungsten, about 07% vanadium, about 0-7%zirconium, the sum total of the added elements Al, C, Co, Fe, Mn, Ni,Si, Ta, W, V, and Zr ranging from about 0-7% by Weight. In a morepreferred embodiment, the above constituents are in the amounts statedexcept that the sum total of the optional elements Al, C, Co, Fe, Mn,Ni, Si, Ta, W, V, and Zr ranges fiom about 2-5%.

In another preferred embodiment, the alloys of this invention compriseabout 10-25% titanium, about 30% chromium, and the balance beingessentially niobium in an amount of at least 50% by weight. In addition,the alloy of this preferred embodiment may contain about 05% ofaluminum, about 02% carbon, about 02% cobalt, about 05% iron, about 05%manganese, about O2% nickel, about 02% silicon, about -0-5% tantalum,about 05% tungsten, about 05% vanadium, about 05% zirconium, the sumtotal'of the added elements Al, C, Co, Fe, Mn, Ni, Si, Ta, W, V, and Zrranging from about 05% by weight.

In a more preferred embodiment, the alloys of this invention compriseabout 15-25% titanium, about In addition to these important uses,v

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28% chromium, and the balance being essentially niobium in an amount-ofat least by weight. In addition, the alloy of this embodiment maycontain about 0- 5% of aluminum, about 0-2% carbon, about 02% cobalt,about O5% iron, about 0-5% manganese, about O2% nickel, about 0-2%silicon, about 0-5% tantalum, about 0-5% tungsten, about 05% vanadium,about 05% zirconium, the sum total of the added elements Al, C, Co, Fe,Mn, Ni, Si, Ta, W, V, and Zr ranging from about 05% by weight, thebalance being niobium in an amount in excess of 50% by weight.

The alloys of this invention may be prepared by conventional metalmelting and remelting techniques using inert conditions. The individualmetals are melted together, solidified and remelted until homogeneity isobtained. The final melt is then allowed to cool and solidify into adesired shape. The case material thus obtained is of a workable metalwith strength and oxidation resistance at high temperatures, and it issuitable as a material of construction in high temperature equipmentdesigned to operate at temperatures beyond the limits of presentequipment constructed of the best high temperature alloys.

These new alloys may be prepared in any of a number of types of meltingfurnaces. The one used in the working examples, 'Which follow, was anarc melting furnace of the type described by W. Kroll in Transactions ofthe Electrochemical Society, vol. 78, pp. 35-47, 1940. This furnace hasan integral, Water-cooled copper crucible in which the charge may bemelted and solidified. The charge of metal constitutents for thisfurnace may be in any convenient form; e.g., powder, shot, wire, sponge,etc. Another suitable melting apparatus is a compressed, consumable arcelectrode furnace as described in US. Patent 2,640,860 to S. A. Herres.Also, one may use a combination of non-consumable and consumableelectrodes in a double melt furnace such as is described in US. Patent2,541,764 to the above-mentioned Mr. Herres. A continuous feed furnacesuch as is described in U.S.P.B. Report 111,083 may also be used.Furthermore, melting could be accomplished by inductively heating thecharge in a suitable crucible. Regardless of the melting apparatus used,care should be exercised to protect the molten metals from the normalatmosphere since contamination of the alloy by oxygen, nitrogen, etc. isto be avoided. To prevent this contamination the melting should becarried out under inert conditions, such as an atmosphere of argon or aprotective slag or a combination of a protective slag and a controlledatmosphere. The practice of using an inert atmosphere when meltingmetals is well known in the art.

The following examples are presented to illustrate the preparation ofspecific alloys of this invention and the outstanding properties ofthese alloys. These examples are illustrative only and are not to beconstrued as limiting the invention. All percents set forth in theensuing examples refer to percents by weight.

EXAMPLE I An alloy of the following composition was prepared: 15titanium, 23% chromium, 59% niobium, 1% tungsten, and 2% tantalum. Theprocedure for preparing this alloy was as follows: The individual metalconstituents were melted together in a furnace having an integral,water-cooled copper crucible, as described by Kroll in the Transactionsof the Electrochemical Society publication referred to above. A heliumatmosphere was maintained, and the alloy composition was alternatelyremelted and solidified six times, whereupon a homogeneous ingot wasobtained.

Table I below sets forth the oxidation resistance possessed by the alloyof this example. Oxidation resistance is determined by the followingprocedure: 7 Weighed samstres at 1200 c. and 1300" c. results or thesetests ti -1200 c.

Table I 7 a =P'ercent weight gain Alloy of Example T 1.5 Unalloyedniobium 20 The Rockwell hardness of the alloy was 48.

The ultimate strength for the alloy of Example I is given below andfor'purposes of comparison data on good, commercially available alloysare also given:

Psi. Ultimate strength at 200,000

. V V H room temp.

Example I {Ultimate strength at 100, 000 1,150 o. p Ultimate strength at103,000 l *oom temp. af Alloy N1 20% Ulggianate'strength at 42, 000Commercial Alloy c: 38% Co, 28% {Ultimate strength at 20,000

512072067 Cr, 7% W, 4% Ti, 2% Fe, 982 0. .ComIIlercialAll0yD:42%Oo,20.5% Ultimate strength at 150,000 Ni, 20% Cr, 4.2% W, 4% Nb, 4% roomtemp.

Mo, 3% Fe, 1.3% Mn, 0.0% si, Ultimate strength at 50,000 0.4% 0. 871 0.

V BXAMPLE'H An alloy of the following composition'was prepared accordingto Example I: 22% titanium, 24% chromium, 51% niobium, 1% cobalt, 0.3%silicon, 1.7% tantalum. p

In the oxidation test described in Example 1 this alloy willshow a 0.9%weight gain, as compared with.20% weight gain for unalloyed niobium. TheRockwell hard ness is 49. The'alloy exhibits an ultimate strength of200,000 psi. at room temperature and 100,O00 p.s.i. at 1150 C. 1 a

. EXAMPLE III Using the procedure 0f Example. I and a charge consistingof 11.2% titanium, 19.2% chromium, and 69.6% niobium, an alloy was madeand tested for ultimate strength at room and elevated temperatures.- Thefollowing data are the results of the tests and a comparison 1 of suchdata good,"com'mercially available alloys:

T able II Ultimate Alloy Composition Temperature Strength, p.s.1.

Alloy A (this 69.6% 10.2% Gr, {9 ttgggg invention). 11.2%11. 1601111195165000 4110 13 80%N1, 20% Cr 421000 Alloy C 38% Go, 28% Ni, 20% 2.O ,000

7 Or, 7% W, 4% Ti, 2% a V Fe,0.2%C.'

Alloy D 42% 00, 20.5% Ni, 20%

. Cr, 4.2% W, 4 Nb, room temp 150,000 4%-Mo, 3% Fe 1.3% 871 0 50,000M11, 0.6% Si, 0 C.

The room'temperature yield strength of applicants Alloy A at 0.2% offsetis 180,000 p.s.i., thus, showing alloy; has useful ductility at roomtemperature. Ad-

- pare with a standard commercial alloy. at the same elevatedtemperature, Alloys A and C of Table Hwere formed intof /z cubesandsubjected to compressive Table III shows the 7 Table IVshowsacompaxisonof results when Alloys 7 'A and C were subjectedtorstress at 1300 C.

Table IV Pressure Applied in Pounds/ -Sq. In. AlloyO j AlloyA (thisinvention) at 1,300" C.' V 7 100,000 p.s.i--...-;. sample crumbledbeforemaximum stress was was applies. 110,000psi anvils crumbled 'but 7 therewas no upsetin the alloy.

Alloy A in the as cast state was subjected to a force in excess of300,000 lbs/sq. in. at 1200 C. as reported in Table III. Examination ofthe microstructure of Alloy A at 250 magnification before it wassubjected to the above force showed that it was composed of two phases,the lighter phase being a continuous phase A scratch test made upon themetal by means of a diamond indenter drawn across the surface underconstant load did not scratch thecontinuous phase, showing that this isthe harder phase. The discontinuous, phase was, however,

scratched, showing it. to. be the softer phase; It is well known in themetallurgical art that fabricability or ductil-ity can be improved ifworking willconvert the'softerphase into a continuous phase; Aftersubjecting Alloy .A

to the above force, the microstructure of the alloy was again examinedat 750smagnification. The working of the .alloy' was found to have.caused the hard continuous phase to be broken into small discontinuousfragments;

It was observed that .the continuous phase the microstructure was thesofter phase, thus indicating an improve: ment in the ductility of themetal.

V "EXAMPLE IV V g V A 155 gram ingot of the renewing composition-wasprepared: 19.2%. chromium,,,11.2 titanium, and 69.6% niobium, by meltingandremelting the metals together 7 ,times in a'water-cooledgcoppercrucible of an' arc melting furnace of the type described; by Kroll inthe.

. vantaneously, it also appears to exhibit a recrys'talliza:

Transactions of the Electrochemical Society publication referred ,toabove. .An atmosphere of helium was used during theheating. When thecharge was in the liquid state, the furnace was turned oifpand the meltwas allowed" to cool inthe helium atmosphere, When. the ingot reachedroom temperature, it was removed from the water-cooled crucible andmachined into a cube which has proved highly successful as a hightemperature forging die.. This alloy has also been made into a hightemperature extrusion die. 7 W

- EXAMPLE- V 26.38% by weight er chromium, 14.72% by weight'of 13.38%titanium, 33.11%

5 titanium, and 68.9% by weight of niobium were charged into the furnaceof Example I. The metals were heated under an atmosphere of helium untilthey were liquid. The melt was then allowed to cool under the heliumatmosphere; and after room temperature was reached, the ingot formed inthe water-cooled crucible was removed. When this alloy was tested forhigh temperature oxidation resistance in the'manner described for TableI, it showed a 0.65% weight gain over the original as-cast weight of thealloy.

EXAMPLE VI Other outstanding alloys within the scope of this inventionmade according to the procedures of Example I are as follows:

22% titanium, 5% chromium, 71% niobium, 2% cobalt: After 16 hoursexposure to air at 1000 C. in accordance with the procedure described inExample I, the gain in weight in the above alloy based on the as castWeight of the ingot was 1.4%.

25% titanium, 2.5% chromium, 68% niobium, 2% nickel,

2.5 aluminum: The above alloy after 16 hours exposure to air at 1000 C.in the procedure described in Example I showed a gain in weight of 1.5%based on the as cast weight of the ingot prior to exposure.

10.86% titanium, 32.41% chromium, balance niobium: The above alloy after16 hours exposure to air at 1000 C. in the procedure described inExample I showed a gainin weight of 0.24% based on the as cast weight ofthe ingot prior to exposure.

19% titanium, 3% chromium, 72% niobium, 2% nickel, 4% manganese: Whenthis alloy was exposed to air for 16 hours at 100 C. in the mannerdescribed in Example I, it showed a 1.55% gain over the as cast Weightof the ingot prior to exposure.

12% titanium, 2.5 chromium, 83.5% niobium, 2%

nickel 25 titanium, 3% chromium, 70% niobium, 2% alumi- 22% titanium, 4%chromium, 70% niobium, 2% nickel,

2% aluminum 5% titanium, 2% chromium, 90% niobium, 0.5% aluminum, 2.5zirconium 17.60% titanium, 7.23% chromium, balance niobium, R

hardness as cast 47 17.87% titanium, 12.19% R hardness as cast 45 17.79%titanium, 17.40% R hardness as cast 46 chromium, balance niobium,

chromium, balance niobium,

chromium, balance niobium, R hardness as cast 47 16.38% 'tanium, 32.56%R hardness as cast 5 8 12.01% titanium, 26.38% R hardness as cast 5517.36% titanium, 22.20% R hardness as cast 48 9% titanium, 10% chromium,balance niobium, R hardness as cast 40 25% titanium, 23% chromium,balance niobium, R

hardness as cast 44 10.35% titanium, 33.11% chromium, balance niobium,

R hardness as cast .60

25 titanium, 25 chromium, balance niobium, R

hardness as cast 50 20% titanium, 28% chromium, balance niobium, R

hardness as cast 52 15% titanium, 30% chromium, balance niobium, R

hardness as cast 55 titanium, 7% chromium, balance niobium, R hardnessas cast 47 chromium, balance niobium,

chromium, balance niobium,

chromium, balance niobium,

Although it is preferable to use metals which are of a high purity, afair amount of variance in purity can be tolerated before productquality suffers appreciably. The alloys of the working examples are madefrom commercially available metals containingless than 1% incidentalimpurities. Commercial niobium nearly always contains tantalum (usuallyin amounts up to 5%) which is hard to detect and very difficult toseparate. Therefore, the niobium used to carry out the specific examplesno doubt contained tantalum which is reported as niobium rather than asan incidental impurity. In addition to the tantalum which is present incommercial niobium, this invention contemplates the addition of tantalumto the alloy composition in amounts up to 7%. Those skilled in the artare readily aware of the presence of incidental impurities in commercialmetals and of the presence of tantalum in commercial niobium, and thesefacts should be taken into consideration when practicing the inventionand construing the claims.

The alloys of this invention may be used as a material of constructionin any structure which requires a strong, corrosion-resistant metal.Particular stress has been laid upon the use of these alloys in hightemperature equipment, such as jet engine parts, nuclear reactor and gasturbine parts because of their outstanding properties. However, itshould be emphasized that use of the alloys of this invention is notlimited to high temperature conditions or to any piece of equipmentdescribed herein.

Since it is obvious that many changes and modifications can be made inthe above-described details without departing from the nature and spiritof the invention, it is to be understood that the invention is not to belimited to said details except as set forth in the appended claims.

This application is a continuation-impart of my copending applicationSerial No. 592,7 05 filed June 4, 1956, now abandoned and also of SerialNo. 593,054, filed June 22, 1956, now abandoned. These latterapplications are in turn continuations in-part of Serial No. 550,764,filed December 2, 1955, now abandoned.

I claim:

1. A high-strength, corrosion-resistant alloy composed of about 530% byWeight of titanium, about 1-30% by weight of chromium, to which may beadded, if desired, up to about 7% by weight of aluminum, up to about 2%by weight of carbon, up to about 2% by weight of cobalt, up to about 7%by Weight of iron, up to about 7% by weight of manganese, up to about 2%by weight of nickel,

up to about 2% by weight of silicon, up to about 7% by weight oftantalum, up to about 7% by weight of tungsten, up to about 7% by weightof vanadium, up to about 7% by weight of zirconium, the sum total of theadded elements Al, C, Co, Fe, Mn, Ni, Si, Ta, W, V and Zr ranging up toabout 7% by weight, the balance being niobium in an amount of at least50% by weight.

2. The alloy of claim 1 in which the sum total of the added elements Al,C, Co, Fe, Mn, Ni, Si, Ta, W, V and Zr range from about 25% by weight.

3. The alloy of claim '1 in which the sum total of the added elementsAl, C, Co, Fe, Mn, Ni, Si, Ta, W, V and Zr is about 2% by weight.

4. A high strength, corrosion-resistant alloy composed of about 530% byWeight of titanium, about 1-30% by weight of chromium, the balance beingessentially niobium in an amount of at least 50% by weight.

5. A high strength, corrosion-resistant alloy composed of about 1025% byweight of titanium, about 1530% by weight of chromium, the balance beingessentially niobium in an amount of at least 50% by Weight.

6. A high-strength, corrosion-resistant alloy composed of about 10-25%by Weight of titanium, about 1530% by weight of chromium, to which maybe added, if desired, up to about 5% by weight of aluminum, up to about2% by Weight of carbon, up to about 2% by weight of cobalt, up to about5% by weight of iron, up to about 5% by weight of manganese, up to about2% by'weight of nickel, up to about 2% .by weight of silicon, up toabout 5% by weight of tantalum, up to about 5% by weight of tungsten, upto about 5% by weight of vanadium, up to about 5% by weight ofzirconium, the sum I 7 total; of the added elementsAl, C, Co, Fe, Mn,Ni, Si, Ta, W, V and Zrranging up to about 5% by weight, the balancebeing niobium in an amount of at least 50% by Weight.

7. A high-strength,corrosion-resistant alloy composed of about 15-25% byweight oftitanium, about 20-28% by weight of chromium, to which may beadded, if desired, up to about 5% by weight of aluminum, up to about 2%by weight of carbon, up to about 2% by weight of cobalt, up to about 5%by weight of iron, up to about 5% by weight of manganese, up to about 2%by Weight of nickel, up to about 2% by weight of silicon, up to about 5%by weight of tantalum, up to about 5%, by Weight of tungsten, up toabout 5% by weight of vanadium, up to about 5% by weight'of'zirconium,the sum total of the 8 added elements Al, C, Co,'Fe, Mn, Ni, Si','Ta, W,V, and Zr ranging up to about 5% by weight, the balance being niobiuminan amount of at least 5Q% by weight. 1-

References Cited in the tile of this patent UNITED STATES PATENTS1,588,518 Brace i v June 15, 1926 1,742,417 Schrobsdorfi Ian. 7, 19302,822,268 Hix Feb. 4, 1958 2,882,146 Rhodin Apr. 14, 1959 FOREIGN,PATENTS V 7 718,822 Germany Mar. 24,1942

1. A HIGH-STRENGTH, CORROSION-RESISTANT ALLOY COMPOSED OF ABOUT 5-30% BYWEIGHT OF TITANIUM, ABOUT 1-30% BY WEIGHT OF CHROMIUM, TO WHICH MAY BEADDED, IF DESIRED, UP TO ABOUT 7% BY WEIGHT OF ALUMINUM, UP TO ABOUT 2%BY WEIGHT OF CARBON, UP TO ABOUT 2% BY WEIGHT OF COBALT, UP TO ABOUT 7%BY WEIGHT OF IRON, UP TO ABOUT 7% BY WEIGHT OF MANGANESE, UP TO ABOUT 2%BY WEIGHT OF NICKEL, UP TO ABOUT 2% WEIGHT OF SILICON, UP TO ABOUT 7% BYWEIGHT OF TANTALUM, UP TO ABOUT 7% BY WEIGHT OF TUNGSTEN, UP TO ABOUT 7%BY WEIGHT OF VANADIUM, UP TO ABOUT 7% BY WEIGHT OF ZIRCONIUM, THE SUMTOTAL OF THE ADDED ELEMENTS, AL, C, CO, FE, MN, NI, SI, TA, W, V, AND ZRRANGING UP TO ABOUT 7% BY WEIGHT, THE BALANCE BEING NIOBIUM IN AN AMOUNTOF AT LEAST 50% BY WEIGHT.